This invention relates to aircraft speedbrakes which are moved to extend into the airstream to increase drag on an aircraft. In particular, this invention uses an exhaust nozzle flap to serve as a speedbrake. As the flap is moved into the airstream, the engine thrust is concurrently spoiled to increase the braking of the aircraft.
Currently many aircraft use flaps which are extended into the airstream as speedbrakes. In commercial aircraft, the flaps are often mounted on the upper surfaces of the wings and lie flush with the wings when not in use. In order to slow down the aircraft, the flaps are extended upwardly from the wing surfaces into the airstream to increase drag on the aircraft.
In military aircraft, the flaps which act as speedbrakes are usually mounted on the airframe. When not in use the flaps lie flush with the surface of the airframe on which they are mounted so as to not cause unnecessary drag on the aircraft. In order to slow down the aircraft or create drag for inflight maneuvers, the flaps are extended into the airstream.
The movement of the flaps which act as speedbrakes, into the airstream is currently independent of the engine controlling flaps. In particular, the movement of the speedbrake flaps does not cause a spoiling of the thrust of the engine.
Modern jet aircraft engines are gas turbine engines which pass combustion discharge gases to the atmosphere at a velocity, and in the required direction, to provide a desired resultant thrust. The exhaust nozzle of the engine has as its purpose the transformation of the pressure and the thermal energy of the combustion discharge or exhaust gases into velocity and thrust.
Exhaust nozzles may be of a variety of types, e.g., fixed area, variable area, convergent, and convergent-divergent. A fixed areas nozzle is only efficient over a narrow range of engine operating conditions. The area of the nozzle is critical, since it affects the backpressure on the turbine and hence the rpm, thrust, and exhaust gas temperature.
Variable area nozzles are often used to maintain a high engine performance under a variety of operating conditions, i.e. the correct balance of pressure and temperature at all operating conditions. In engines with afterburners, variable area nozzles are required. The area of an afterburning jet pipe is larger than a normal jet pipe for the same engine. The nozzle is narrowed when the afterburners are off and is opened when the afterburners are on to give an exit area suitable for the increased volume of the gas stream.
Convergent nozzles are designed to maintain a constant internal pressure and still produce sonic velocities at the nozzle exit. In this type of nozzle the gas flow is subsonic as it leaves the turbine. In a convergent nozzle, the gas velocity cannot exceed the speed of sound. In order for the gas to exceed the speed of sound, a convergent-divergent nozzle must be used. In the diverging section, the speed of the gas is increased to supersonic speed by increasing the gas volume outwardly and rearwardly while controlling the direction of the gas expansion.
Variable area nozzles have used a variety of flaps at the exit ends of the nozzles to vary the exit areas. One example of flaps for varying the area of exit from a convergent nozzle is shown in U.S. Pat. No. 3,386,247, issued Jun. 4, 1968 to the assignee of the present invention, for a "Powerplant with Thrust Reversers". Hinged flaps are provided which are moved toward and away from the centerline of the engine to vary the nozzle area. The flaps are opened to spoil the thrust of the engine during thrust reversal, but are not used as speedbrakes, nor do they spoil the thrust in flight.
If the functions of the flaps which act as speedbrakes can be combined with the functions of the flaps which control the exhaust nozzle, this would be a beneficial improvement. This improvement would be particularly beneficial if activation of the speedbrakes also acts to spoil the thrust of the engine simultaneously.